1. Field of the Invention
The present invention pertains to voltage leakage detection in seismic electrical systems and, more particularly, leakage detection seismic surveying systems comprising serially connected nodes.
2. Description of the Related Art
Seismic surveying is a method for determining the structure of subterranean formations in the earth. Seismic surveying typically utilizes seismic energy sources which generate seismic waves and seismic receivers which detect seismic waves. The seismic waves propagate into the formations in the earth, where a portion of the waves reflects from interfaces between subterranean formations. The seismic receivers detect the reflected seismic waves and convert the reflected waves into representative electrical signals. The signals are typically transmitted by electrical, optical, radio or other means to devices which record the signals. Through analysis of the recorded signals (or traces), the shape, position and composition of the subterranean formations can be determined.
One concern in a land-based seismic survey is “earth leakage”, a condition which may expose a person or animal to dangerous voltage levels. A seismic survey system is typically laid out with a series of units connected together by a seismic cable in between. Cables, connectors and units transferring or relaying electrical power in a seismic survey system are subject to earth leakage situations. There can be several hundred units in each power domain and 10s of meters of cable between them, making the whole power domain span several kilometers. Thus, not only are there typically a very large number of places in which earth leakage might occur, but they usually are spread out over large distances. Locating and fixing an earth leakage condition can therefore be a time consuming and difficult task.
Seismic survey systems therefore usually provide for some kind of automatic detection of and protection from earth leakage. Conventional earth leakage detection/protection systems introduce a ground wire and force the output voltage to balance around earth. The current in the ground wire should nominally be close to, or at, zero. This current is monitored, and if it increases beyond a set limit, switches turn off the voltage to the whole power domain.
Conventional earth leakage detection and protection systems, although helpful and desirable, have several drawbacks. When an earth leakage occurs, the whole line of units in the affected power domain loses power. There is no way to automatically diagnose where along the line the earth leakage is located, meaning it will take a long time to find the faulty segment. Intermittent failures that come and go and failures of short duration are even harder to find unless the system is taken back to camp and tested in a water tank or similar apparatus. Thus, while such systems are suitable for their intended purpose, improvement in these respects would be desirable.
The present invention is directed to resolving, or at least reducing, one or all of the problems mentioned above.